It is well known in motor vehicles to restrain a seated occupant with a seat belt assembly such as a conventional three-point seat belt. The three-point seat belt typically includes a lap belt and a shoulder belt, which reach around and thereby secure the occupant to the car seat. The seat belt assembly may also include a seat belt tensioning device or pre-tensioner, which forcibly tensions the seat belt in response to a vehicle condition such as vehicle deceleration or an impact.